Rescuers were quickly on the scene of the crash
Human error is being blamed for a train collision on the outskirts of Los Angeles, California, which has claimed the lives of at least 24 people.
The driver of a train with 222 passengers aboard apparently ignored a red signal, causing it to hit a freight train head on, the rail company says.
The passenger train hit the freight train with such force, its engine was shoved back inside the first carriage.
Officials say the chances of finding any further survivors are very remote.
Firefighters have cut through the roof of the train, which is a double-decker, removing chunks of metal piece by piece.
Sniffer dogs have been brought in to try to detect any signs of life.
A spokeswoman for the rail company Metrolink, Denise Tyrrell, told reporters:
"At this moment we must acknowledge that it was a Metrolink engineer that made the error that caused yesterday's accident."
It was not immediately clear whether the driver had survived.
The death toll is expected to rise as more bodies are uncovered. More than 80 people are in hospital.
The worst rail crash in the US for 15 years happened at 1632 local time (2332 GMT) on Friday, at a time when the passenger train was carrying 222 people, most of them commuters.
The passenger train was travelling from Los Angeles to Moorpark, north-west of the city.
It collided with a Union Pacific freight train on a curving stretch of track in Chatsworth, in the San Fernando Valley area of Los Angeles county.
The front coach of the Metrolink passenger train derailed and was crushed by the engine after the collision. Two other coaches of the train remained upright.
Aerial images of the crash scene showed teams of rescuers using ladders to reach injured people inside the mangled front coach.
The Union Pacific freight train was badly damaged in the accident. Officials say two people - the driver and the conductor - were on board the train.
"I heard a loud crash and I saw black smoke... some people were mangled pretty bad," Phil Thiele, one of the passengers in the front coach, told the Los Angeles Times.
He said he tried to help one man who was pinned between seats: "I tried my damnedest to get him out but I just couldn't."